Frequently in crowded urban office environments, volatile air-borne contaminants contribute to a variety of undesirable effects on persons and property, collectively sometimes referred to as "sick building syndrome". These contaminants issue from various synthetic building materials, from contaminated heating, ventilation, and air conditioning ducts, and from a variety of electrical and electronic devices. A frequent and significant contributor to air contamination, and thus to "sick building syndrome" is ozone. Ozone is a very active form of oxygen molecule, and is produced in office buildings by electronic copiers, laser jet printers, and other electrical and electronic equipment. It is also produced by devices which use ultraviolet light, often for sterilization of medical and dental instruments, sterilization of deionized process water, sterilization of equipment used for hair care and other applications in cosmetology and skin care, and for surface activation of polymers and other manufacturing processes.
Ozone is a toxic gas that has an unpleasant, pungent odor that is detectable at concentrations as low as 0.05 parts per million (ppm). It becomes irritating to the eyes, nose, and lungs at about 0.1 ppm. The American Conference of Governmental and Industrial Hygienists (ACGIH) and the Occupational Safety and Health Administration (OSHA) have extablished the maximum permissible average concentration of ozone as 0.1 ppm over an eight hour exposure period.
Conventional methods for reducing ozone concentrations in air use activated carbon alone or in combination with metal catalysts or oxide catalysts such as activated manganese dioxide and high surface area ferric oxide. Examples of activated carbon filters that are available commercially are the "TAK Filter 800 Cell" produced by Roki Company in Tokyo, Japan, and a honeycomb activated carbon filter produced by Ricoh Co. in West Caldwell, New Jersey. These activated filters have been found to lose approximately one half their ozone decomposing capacity after about 1 days' service. U.S. Pat. No. 5,256,377 entitled "Ozone Decomposing Material and Ozone Decomposing Apparatus Using the Ozone Decomposing Material", issued Oct. 26, 1993 discusses this degradation issue. To overcome the loss of ozone decomposing capacity this patent claims the use of a number of dipentene compounds in combination with an activated carbon filter.
Because conventional air filters for reducing ozone made of activated carbon alone or with catalysts lose approximately one half their ozone decomposing capacity after just one day in service, and because these filters cost approximately $100 for one of a size suitable for an office copier or printer, an effort was undertaken to find or produce an ozone decomposing filter which is effective at decomposing ozone over a much longer period and at a greatly reduced cost. The present invention arose from that effort.
The present invention is a monolithic carbon composite filter and a simple, inexpensive method for producing it. The filter has been tested for ozone destroying capacity and has been found to be extremely effective. Moreover, this filter has a long ozone-decomposing lifetime without the use of catalysts or adsorbed dipentenes. Precursor materials are inexpensive, non-hazardous, and readily available. The method permits easy casting-to-shape of a monolithic filter.